British Pat. No. 1,073,741, describes a method for preparing flat or tubular net-shaped or netlike structures consisting of interconnected, longitudinally oriented, synthetic polymer filaments, by producing, with the help of suitable cutting devices, a series of parallel and distanced fissures or slots in a flat or tubular, mono-oriented polymeric film, so that the successive transversal expansion of the film would create such a netlike structure.
Netlike structures of a similar type, though formed by filaments interconnected with each other in a more irregular and casual way, may be achieved, moreover, by disgregation (breaking up) or slitting mono-oriented polymeric films by different method, such as, for instance, by sandblasting, brushing or rubbing.
The products thus obtanined, in general, are bulky and flexible and display a specific surface area of up to 10 to 12 m.sup.2 /g. the thickness thereof in microns. They are used in the manufacture of ropes, strings and textile materials of various kinds.
Spanish Pat. No. 460,292 disclosed use of structures of this type, opened by cross-expansion, in inoragnic hydrosetting binder-based mixes, in order to improve their mechanical characteristics.
Given the chemical incompatibility of synthetic polymers in general toward the inorganic materials that form the hydrosetting binders, the polymeric structures thus used, hardly adhere to the matrix of the binder and, therefore, the reinforcing effect is not altogether effective.